This application relates to an axial pawl ratchet mechanism and in particular, to an axial pawl mechanism used with a hand tool or power tool to provide for application of torque in order to tighten or loosen a fastener.
Radial pawl systems are known for ratcheting mechanisms. A gear having peripheral teeth is mounted within the head of a tool and a pawl, formed as an individual finger, is pivotally mounted at the periphery of the gear. The pawl is biased into engagement with one or two teeth of the gear and when the head is rotated in one direction, transmits head rotation to the gear and when the head is rotated in the opposite direction, allows the head to undergo ratcheting rotation relative to the gear. The pawl generally includes a spring on either side in order to return the pawl to the engaged position against the teeth of the gear. In other embodiments, a radial pawl is provided which is a generally semicircular shaped disc having pawls formed by top corners of the disc. For example, U.S. Pat. No. 6,109,141 provides a reversible pawl disc that pivots between a first position, allowing ratcheting rotation in a first direction, and a second position, allowing for ratcheting rotation in a second direction. Such ratcheting pawl mechanisms have one to four teeth of the pawl engageable with the gear. Therefore, there is much vibration applied to a few teeth. As well, when the pawl engages the gear, in order to prevent rotation, there is a great amount of pressure against the teeth of the pawl. Therefore, such ratchet mechanisms provide a great amount of wear on the pawl and the lifetime of such pawls is limited.
While some pawl mechanisms are known that have teeth extending axially around the face of the disc, such systems have been very limited in their use and are not adaptable for use in most hand tools or power tools. Axial gear teeth of some prior art mechanisms are not easily adapted for bidirectional use. For example, U.S. Pat. No. 4,479,409 discloses a hand wrench having a crescent-shaped head portion having axial teeth formed on both sides. In order to provide for bidirectional ratcheting, the head portion must be removed completely from the wrench, inverted, and replaced on the wrench in the inverted position to provide for ratcheting in the opposite direction. Such a device is cumbersome to use and allows for the possibility that the head portion may be lost or displaced from the wrench.
Other currently available ratchets may backstop the drive body to the housing for chatter free operation, but require inversion for changing drive direction. Still other powered ratchets are directionally selectable through radially acting, symmetrical, pivoting pawls, but use varying degrees of friction for backstopping—the frictional approach being inefficient, less than 100% effective, a maintenance problem and inherently lacking the strength required for typical uses.